The present invention relates to endless transmission belts and, in particular, to endless belts for use in continuously variable transmissions of the chain type in which a number of link plates are interconnected in an endless manner.
FIGS. 1 (a) and (b) are views showing the overall structure of parts of the conventional transmission belt, FIG. 1 (a) showing a portion in a straight run of the belt, i.e., in a portion which is not in engagement with the pulleys, and FIG. 1 (b) showing a bent portion of the belt, i.e., in a portion which is in engagement with a pulley. FIG. 2 is a side view showing the state of blocks and pins in contact with a driving pulley during operation of the belt, and FIG. 3 is a sectional view showing the state of the belt when engaged with a pulley. FIG. 2 shows the nontorque transmitting region a and the torque transmitting region b when rotation is counterclockwise as indicated by arrow R.
As shown in FIGS. 1 and 2, a first block 1 and a second block 2 each have a groove 4 engaging a pin 3 and having a generally rectangular shape partially defined by a flat side surfaces 1a or 2a. In order to allow the pin 3 to can't whereby the inner side of a pin projects by an amount .DELTA. beyond the space normally occupied by the pin, as when the belt passes around a pulley, gaps corresponding to (2.times..DELTA.) must be provided between the pins 3 and the blocks 1 and 2 when these members are present in a straight portion of the belt. The dimension of the gap has to be determined using an amount .DELTA. by which the pin projects when the belt is bent at the minimum rotational radius. As a result, if the rotational radius of the belt is larger than the minimum rotational radius, a gap X may occur in the bent portion of the belt even in the non-torque transmitting region a, as shown in FIG. 2. In FIGS. 1 and 2, reference numerals 5 and 5' denote links engaging with the pins 3 and 3', and reference numeral 6 denotes a portion of contact between pins 3 and 3' and the grooves 4 and 4' of the blacks.
The occurrence of such gaps X leads to the following problems:
(1) The blocks 1 and 2 may slip a distance corresponding to the gaps X when the belt is in engagement with pulleys 7 (see FIG. 3), thereby making the surfaces of contact between the pulleys 7 and the blocks 1 and 2 more vulnerable to wear, and causing a reduction in transmission efficiency.
(2) When the belt is in engagement with the pulleys 7, since the blocks 1' and 2' are inclined relative to the axis 8 of the pulleys 7, which inclination leads to abrasion of the surfaces of the pulleys 7. In FIG. 3, reference numerals 3' and 9 denote pins and sets of link plates, respectively.
(3) In a straight portion of the belt, string vibration of the belt causes an increase in the chattering movement of the blocks 1 and 2, resulting in the generation of more noise.